Effect of aging on the spectral response of transformer oil

Recent studies have characterized the response of the absorption of transformer oil to in-service and laboratory aged transformer oils. The results, established using a laboratory grade spectrophotometer, indicate that both for transformer oil degraded in the laboratory and for transformer oil drawn from transformers that have been in service for extended periods of time, the transformer oil absorbance increases by a significant and easily observable margin over a range of wavelengths. This result is substantiated by theoretical analysis of the products of the aging process. The aging processes explored include degradation by arcing, thermal stress and excessive exposure to atmospheric air. Based on the spectral absorption characteristic, a novel methodology for on-line transformer health assessment using ultraviolet absorption was developed. The new system, an optical monitor for the health assessment of power transformers, provides an alternative or complement to on-line dissolved gas analysis for predictive maintenance programs. The measurements performed with the prototype system are validated with a spectrophotometry measurement and an independent oil testing laboratory.